1. Field of the Invention
The present invention relates generally to a bearing, and more particularly, to a crossed-roller bearing.
2. Description of the Related Art
A conventional crossed-roller bearing is composed of a plurality of rollers crosswise mounted between an inner ring and an outer ring to allow itself to bear radial, axial, and momental loads. Compared with the general bearing, the crossed-roller bearing is particularly applicable to the circumstances, like tool machines and mechanical arms, in need of high rigidity and rotational accuracy. As disclosed in each of the patents, like Japan Patent Pub. Nos. 2000-65080, 2000-170754, 2002-13540 & 2005-180578, the insertion hole for installing rollers is designed to be perpendicular to the raceway. In this way, two raceway surfaces are formed on each of the bearings and become broken because of the insertion hole, so the loading capacity of the bearing with two broken raceway surfaces is less than that of the bearing with one broken raceway surface.
In addition, the plug adapted to fill the insertion hole should flush with the raceway surfaces under optimal circumstances to keep the raceway surfaces flat. However, the processing inaccuracy still results in roughness between the plug and the raceway surfaces. As far as the conventional crossed-roller bearing is concerned, the plug needs to be designed to make up for the raceway surfaces; otherwise, it tends to happen that the plug flushes with one of the raceway surfaces but the other raceway surface is still rough; namely, the raceway surfaces are very likely rough. Besides, the plug for the aforesaid crossed-roller bearing needs to be processed to have a V-shaped complex hyperboloid in harmony with the raceway surfaces, so such processing is more expensive than that of one single curved surface.